The goal of this project is to generate recombinants of the enveloped virus, vesicular stomatitis virus (VSV) encoding HIV 89.6 Env protein and SIVmac239 Gag protein, characterize the immune responses to these viruses in rhesus macaques after mucosal and intramuscular immunization, and evaluate protection of the monkeys from a challenge with a pathogenic SIV/HIV hybrid, SHIV-89.6P. In addition to encoding the SIV and HIV proteins, the viruses to be constructed will have envelopes from either of the two VSV serotypes or from a second vesiculovirus. The use of the different envelopes will allow boosting without neutralization of the vector itself. Dr. Rose's laboratory has pioneered the development of VSV as a vector, and has shown that VSV recombinants encoding an influenza hemagglutinin protein are potent live intranasal vaccines that protect mice against a lethal challenge with influenza virus. VSV vectors can be used to express large amounts of foreign genetic information including genes encoding complete HIV Env and Gag proteins. The VSV/HIV env viruses induce CTLs to HIV Env protein as well as HIV neutralizing antibodies in mice. Drs. Marx and Nixon (who are co- investigators on this application) have obtained preliminary results showing strong antibody and CTL responses to HIV Env encoded by a live VSV vector in rhesus macaques in the absence of detectable pathogenesis. The proposed study will examine in detail the immune responses in rhesus macaques to HSV vectors (total antibody, HIV neutralizing antibody, VSV neutralizing antibody, and quantitative CTL precursor frequencies to Env and Gag and to VSV nucleocapsid protein. Sufficient animals will be used to allow comparison of short-term and long-term immunization protocols and for a pathogenic SHIV challenge experiment with sufficient controls. The SHIV challenge will be followed by quantitative analysis of viral load, health, and immune status of the vaccinated and control animals.